1. Field
The disclosure relates to a method, system, and article of manufacture for exchanging locations of an out of synchronization indicator and a change recording indicator via pointers.
2. Background
Certain mirroring mechanisms provide data replication over extended distances between two sites for disaster recovery. If adequate bandwidth exists, such mirroring mechanisms may provide a recovery point objective of as low as 3-5 seconds or less between the two sites at extended distances, with no performance impact on the application at the primary site. Certain mirroring mechanisms may copy the data asynchronously and also forms a consistency group at a regular interval, allowing a clean recovery of data.
Certain mirroring mechanisms may pause updates of the primary volumes and then use a bitmap to drain updates from the primary volumes to the secondary volumes at the remote site. After all primary updates have been drained, the secondary volumes are used as the source for a point in time copy to tertiary volumes at the recovery site. This ensures that the tertiary copy of the volumes has a point-in-time consistency. By grouping many volumes into a single session, multiple volumes may be copied to the recovery site simultaneously, while maintaining point-in-time consistency across those volumes.
Such mirroring mechanisms can control the formation of consistency groups for data consistency. A consistency group is a collection of volumes across multiple storage units that are managed together when creating consistent copies of data. The order of dependent writes is preserved in consistency groups. The formation of these consistency groups may be controlled by a primary storage unit, which sends commands over remote mirror and copy volumes to remote storage units.